Just how big, they never imagined. On Wednesday, Sam Van Duhn and his two friends, Ryan Roberts and Tony Musca, took a father-and-son fishing trip off of longboat pass on the Double Nickel charter boat.

Mark Van Duhn – Father: "What we said to the boys is, ’You have a choice, you can either man the amberjack rod or you can man the shark rod.’ And they said, 'We want the shark.'"

The, around 11:30 in the morning, 20 miles out in 100 feet of water, something bites their 15 pound amberjack bait.

Sam Van Duhn: "Everyone started screaming and yelling, 'Yay! We got a shark!'"

Mark Van Duhn: "Just a battle of wills between the shark and 12 year-old young men."

Boys win, and the shark is towed back to shore - a female shark weighing 692 pounds. The 692-pound Mako Shark is a big catch for Mote Marine researchers too. They will study the skin and fin samples to better understand what makes the Mako the fastest swimming shark.

Dr. Robert Hueter - Director, Center for Shark Research at Mote Marine Laboratories: "They can get up to 30 miles per hour cruising speed."

Hueter says the study's findings may help make underwater crafts, even airplanes faster. As for finding these large predators in the Gulf, Hueter says it's not unusual.

Dr. Robert Heuter: "No. Beach-goers should not be concerned at all with this. We're talking about an animal that is an oceanic species, not coastal species."